Certain continuously extruded products, e.g. vinyl fluid hose, must be cooled immediately after passing through the extrusion operation in order to prevent deformation. In the case of vinyl hose, because of the retained heat in the extruded product, the hose becomes susceptible to damage in handling which in turn leads to excessive rates of rejection of the manufactured or extruded hose. In conventional extrusion operations where the extruded material, be it hose, rod, bar or any other shape that would deform of its own weight if the temperature was not decreased rapidly after extrusion, cooling by immersing the extrudate in a water bath, which bath is placed downstream and as close as possible to the exit of the extrusion apparatus is utilized.
In the manufacture of braided hose which takes place by using a cooling step to cool the soft inner liner of the hose prior to braiding so that the inner liner is not deformed or the braid sinks into and becomes imbeded in the outer surface of the soft inner liner, a cryogenic cooling chamber such as disclosed in U.S. Pat. Nos. 4,654,107 or 4,654,094 is utilized. Both of the foregoing patent specifications and the discussion of the prior art therein are incorporated herein by reference. In utilization of a water cooling step following the extrusion, a problem results from the limitation on extrusion speed because of the fact that the water bath has a well defined heat transfer capability and thus can only cool the fresh extrudate in accordance therewith. Attempts have been made to increase the size of the bath and use associated refrigeration of the bath with little success in markedly increasing the extrusion speed.
The device of the '094 and '107 patents provides a more rapid method of cooling the extrudate except that direct contact of the cryogen, e.g. liquid nitrogen, on the extruded material results in uneven temperature gradients across the extrudate which in turn causes distortion and/or internal damage to the extrudate. Furthermore, such a device does not fully utilize both the liquid and gaseous refrigerant. Lastly, such a device relies upon material convection rather than mechanically forced convection and if the extrudate freezes, either due to its own material seizing to the tube, which is the central part of the chamber, or moisture freezes inside the chamber causing an ice buildup, the system is extremely difficult to clean and restart.
Furthermore, the water immersion process does not allow for speed increases necessary because water is carried along on the extrudate surface, thus the moisture may not evaporate entirely, causing defects in the final extruded product.